The Free On-line Dictionary of Computing (30 December 2018):

Systems Network Architecture
Blue Glue
SNA

    (SNA) IBM's proprietary high level networking
   protocol standard, used by IBM and IBM compatible
   mainframes.

   Also referred to as "Blue Glue", SNA is a bletcherous protocol
   once widely favoured at commercial shops.  The official IBM
   definition is "that which binds blue boxes together."  It may
   be relevant that Blue Glue is also a 3M product commonly
   used to hold down carpets in dinosaur pens.

   [Jargon File]

   (1994-11-23)